One of my favorite Michigan authors the late Elmore Leonard promoted the idea of always administering a “kill shot.”
Not leaving an unconscious lackey who later would wake up and take a hostage. Not a POS who had to be given medical treatment and recovery in a hospital. Dead.
A better reason is that if the suspect is merely wounded, there will be two stories out there, and if in the US, likely to hire a lawyer to sue.
If the suspect is dead, the cops are only going to hear one story - yours, and a civil suit is much less likely (although not impossible from a relative hiring a shyster).